CMV status of the donor and the recipient influence the outcome of allogeneic stem cell transplantation. To study factors determining CMV status, 40,311 patients and 23,048 donors were identified in the EBMT registry. Logistic regression models predicting seropositivity were constructed. Female patients were more likely to be seropositive (p< 0.001). The risk increased with age (p< 0.001) but decreased according to the year of transplant (p< 0.001). There were differences in the probability of seropositivity between patients from different countries. Adjusted for patient serostatus, the risk of a donor being seropositive was higher in females (p< 0.001) and older donors (p< 0.001).